Thermosensitive bulb



Nw., M49 A. ZUEHLKE THERMOSENSTIVE BULB Filed Jan. 6, 1948 FME. A@

Tl M E lNI/ENTR. MHTHU A. UEMMQM Patented Nov. 8, 1949 @UNITED s'rATlzsPATENT OFFICE THERMOSENSITIVE BULB Arthur A. Zuehlke, Rochester, N. Y.,assigner to Taylor Instrument Companies, Rochester, N. Y., a corporationof NewYork Application January 6, 1948, Serial No. 718

8 Claims.

This invention relates to a thermosensitive device and more particularlyto a bulb for use in such a device. y

In many installations, it is highly desirable that the bulbs of suchdevices have exceedingly fast speeds of response so that any deviationfrom a required temperature can'be promptly detected.

The presentv invention has for its purpose a novel construction ofthermosensitive bulb having a greatly improved speed of response ascompared with conventional types.

The main feature of the invention relates to a thermosensitive bulb' inwhich the walls thereoi' consist of bimetallic material, that is layersof dissimilar metals bonded together and having diiferent coefilcientsof expansion.

Various other features and advantages of the invention will appear fromthe detailed descriptien and claims when taken with the drawin in which:y

Fig. 1 discloses the bulb of the present invention incorporated in athermosensitive tube system;

Fig. 2 is a cross-section of the bulb of Fig. 1 taken on the line 2-2thereof;

Figs. 3, 4, 5 and 6 are cross-sections similar to that of Fig. 2 butshowing various modied forms of construction; and

Fig. 'l is a chart useful in describing the inven-V tion.

Referring first to'Fig. 1, there is illustrated a thermosensitive tubesystem comprising the bulb 5 of the present invention which communicatesthrough a capillary tube 6 with a pressure responsive element such as aconventional Bourdon spring 1. The inner end of the Bourdon spring ismounted on a fixedV support 8 while the outer or free end of this springis provided with a suitable take-oil arm S. This arm has pivoted theretoa link i connectible to a movable index or control element (not shown).The tube system may be lled with any oi the well-known fluid fillingmediums so that this iluid causes the Bourdon spring l to wind-up or tounwind, as the case may be when the temperature at the bulb changes.

In accordance with the present invention, the bulb 5 is made ofbimetallic sheet material consisting of two layers of metal 5A and 5Bbonded together,` the metal layers having two different coeiliients ofexpansion. This bulb can conveniently be made from a short piece ofbimetallic tubing by iiattening the piece and suitably sealing its ends,preferably the space between the opposed inner suriaces of flattenedbulb being somewhat thinner than the thickness o'f one of the layers 5Aand 5B. The capillary tube G will of course be sealed to one end of thesealed piece in communication with the interior thereof. It will beunderstood that when these layers are subjected to a change intemperature, they will expand differentially to change promptly thevolume of the bulb so that the fluid in the tube system will cause theBourdon spring to Wind-up or unwind as the case may be.

In the construction of Fig. 3, the layer of metal having the greatercoeiiicient of expansion is located at the outer surface of the bulbwith the metal layer having a lower coeicient of expansion at the innersurface thereof. In this construction, the volume of the bulb expands onan increase in temperature as shown by the convex shape of its sides.Similarly, the volume of the bulb contracts on a decrease intemperature.

In the construction of Fig. 4, the layer of metal having the greatercoefficient of expansion is 1ocated at the inner surface of the bulb,While the metal layer having the lower coeiiicient of expansion islocated at the outer surface of the bulb. In this construction, the bulbwill contract on a rise in temperature so that its sides will beconcave, as illustrated. AA'drop in temperature will cause the bulb toexpand with its sides convex.

As shown in Fig. 5, the bulb can be made of -two bimetal strips eachcomprising the layers 5A and 5B having different coeiiicients ofexpansion. The edges and ends of these strips can be welded directlytogether or they can be Welded to a metal bead I2.

The bulb can also be made from la single bimetallic strip bent into theU-shaped cross-section of Fig. 6, with the free edges thereof weldedtogether or to a bead I3.

The operation of the several bulbs, herein shown, will best beunderstood by reference to the chart designated Fig. '7. When atemperature change is impressed on the bulb 5, the two sides of the bulbchange in shape and thereby change the internal volume of the bulb. Thechange in volume due to the change in shape of the bulb will be largerthan the change in internal volume of the liquid due to its expansionwith temperature. A typical ratio of these two volume changes is ten toone.

That the bulb of the presentinvention is much faster in response thanthel conventional bulb is due to the fact that the majority of theresponse is controlled by the relatively thin shell comprising themetallic part ofY the bulb. In

other words, when the metallic layers are heated through, the largestportion of the response has taken place. This is in contrast to aconventional bulb in which the speed of response is controlled for themost part by the rate of heating of the liquid volume inside the bulb.

It is the nature of this particular invention that the volume change duetothe metallic portion of the bulb (see curve A of Fig. 7) and thevolume change due to the liquid expansion within the bulb (see curve B)influences the Bourdon spring or other pressure responsive element inopposing directions, that is, the resultant magnitude of response of theBourdon spring is equal to the difference between the two mentionedvolumetric effects (see curve C). It will be noted that the resultingresponse curve C is different from conventional responses in that theresponse first reaches a maximum andthen declines a small degree.

While the Bourdon spring type of pressure responsive element has beendisclosed, it will be understood that other pressure responsive elementssuch as bellows, diaphragms and capsular chambers may be substitutedtherefore.

Although any type of bimetallic material may be used, it is convenientto use that type wherein one of the metal layers thereof hassubstantially zero coefficient of expansion.

What I claim is:

l. A sealed bulb for use in a thermoresponsive tube system wherein thebulb is sealed in communication with a capillary tube in turncommunicating with a pressure responsive element, the tube system beingfilled with a transmitting fluid, said sealed bulb comprising twoopposing walls, each made of two layers bonded together throughout theirentire area, said layers having different coefficients of expansion, thespace between the inner surfaces of said opposing walls being thinnerthan the thickness of one of said layers whereby the volume change ofthe bulb in response to a given temperature change is substantiallygreater than the volume change of the fluid therein in response to saidgiven temperature change.

2. A thin, flat bulb adapted to be filled with a thermoresponsive fluidfor communication with the capillary tube of a thermoresponsive device,said bulb comprising an elongated tube flattened into strip form withsealed ends except for anp opening in one end in communication with thecapillary tube and having opposed walls, each wall being made ofbimetallic layers bonded together throughout a substantial area thereof.

3. A thin, flat, strip-type bulb adapted to be nlled with athermoresponsive fluid for communication with the capillary tube of afluid filled thermoresponsive device, said bulb comprising an elongatedtube made entirely of two layers of dissimilar metals bonded togetherand flattened into band-like form with sealed ends except for an openingin one end for communication with said capillary tube.

4. A flat, strip-type bulb filled with a thermoresponsive nuld forcommunication with the capillary tube oi a fluid-filled thermoresponsivedevice, said bulb comprising two elongated, opposed, strip-like wallseach made of bimetalllc layers with a thin space between them, said layytion with the capillary tube of a iluid-fllled thermoresponsive device,said bulb comprising two opposed walls each made of bimetallic layerswith a thin space between them, said layers having diiferentcoeillcients of expansion, the layer having the greater coefficient ofexpansion being located at the outer surface of the bulb.

6. A flat strip-type bulb filled with a thermoresponsive fluid forcommunication with a capillary tube of a fluid-filled thermoresponsivedevice comprising a bimetallic strip, U-shaped in cross section andhaving its edges joined together in sealed relation.

7. A fiat strip-type bulb adapted to be filled with a thermoresponsivefluid for communication with a capillary tube of a fluid-filledthermoresponsive device, said bulb comprising two opposing bimetallicstrips connected together at two adjacent edges sealed at their endsexcept for an opening in one end in communication with the capillarytube and a bead to which the remaining adjacent edges of said strips arewelded in sealed relation.

8. A sealed bulb for use in a thermoresponsive tube system wherein thebulb is sealed in communication with a capillary tube in turncommunicating with a pressure responsive element, the tube system beingfllled with a transmitting fluid, said sealed bulb comprising twostrip-like opposing walls, each made of two layers bonded togetherthroughout their entire area, said layers having different coeillcientsof expansion, the space between the inner surfaces of said opposingwalls being thinner than the thickness ol' one of said layers wherebythe volume change of the bulb in response to a given temperature changeis substantially greater than the volume change of the fluid therein inresponse to said given temperature change.

ARTHUR A. ZUEHLKE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,544,342 Phelan June 30, 19251,657,353 Francke Jan. 24, 1928 1,736,984 Sheats Nov. 26, 1929 2,029,038yScott Jan. 28, 1936 2,392,613 Persons Jan. 8, 1946

